32 research outputs found
On the computation of preliminary orbits for Earth satellites with radar observations
We introduce a new method to perform preliminary orbit determination
for satellites on low Earth orbits (LEO). This method works with
tracks of radar observations: each track is composed by
topocentric position vectors per pass of the satellite, taken at
very short time intervals. We assume very accurate values for the
range , while the angular positions (i.e. the line of sight,
given by the pointing of the antenna) are less accurate. We wish to
correct the errors in the angular positions already in the
computation of a preliminary orbit. With the information contained
in a pair of radar tracks, using the laws of the two-body dynamics,
we can write 8 equations in 8 unknowns. The unknowns are the
components of the topocentric velocity orthogonal to the line of
sight at the two mean epochs of the tracks, and the corrections
to be applied to the angular positions. We take advantage
of the fact that the components of are typically small.
We show the results of some tests, performed with simulated
observations, and compare this method with Gibbs'
and the Keplerian integral
Innovative observing strategy and orbit determination for Low Earth Orbit Space Debris
We present the results of a large scale simulation, reproducing the behavior
of a data center for the build-up and maintenance of a complete catalog of
space debris in the upper part of the low Earth orbits region (LEO). The
purpose is to determine the performances of a network of advanced optical
sensors, through the use of the newest orbit determination algorithms developed
by the Department of Mathematics of Pisa (DM). Such a network has been proposed
to ESA in the Space Situational Awareness (SSA) framework by Carlo Gavazzi
Space SpA (CGS), Istituto Nazionale di Astrofisica (INAF), DM, and Istituto di
Scienza e Tecnologie dell'Informazione (ISTI-CNR). The conclusion is that it is
possible to use a network of optical sensors to build up a catalog containing
more than 98% of the objects with perigee height between 1100 and 2000 km,
which would be observable by a reference radar system selected as comparison.
It is also possible to maintain such a catalog within the accuracy requirements
motivated by collision avoidance, and to detect catastrophic fragmentation
events. However, such results depend upon specific assumptions on the sensor
and on the software technologies
Orbit Determination with the two-body Integrals
We investigate a method to compute a finite set of preliminary orbits for
solar system bodies using the first integrals of the Kepler problem. This
method is thought for the applications to the modern sets of astrometric
observations, where often the information contained in the observations allows
only to compute, by interpolation, two angular positions of the observed body
and their time derivatives at a given epoch; we call this set of data
attributable. Given two attributables of the same body at two different epochs
we can use the energy and angular momentum integrals of the two-body problem to
write a system of polynomial equations for the topocentric distance and the
radial velocity at the two epochs. We define two different algorithms for the
computation of the solutions, based on different ways to perform elimination of
variables and obtain a univariate polynomial. Moreover we use the redundancy of
the data to test the hypothesis that two attributables belong to the same body
(linkage problem). It is also possible to compute a covariance matrix,
describing the uncertainty of the preliminary orbits which results from the
observation error statistics. The performance of this method has been
investigated by using a large set of simulated observations of the Pan-STARRS
project.Comment: 23 pages, 1 figur
Innovative system of very wide field optical sensors for space surveillance in the LEO region
ABSTRACT We present the results of a large scale simulation, reproducing the behavior of a data center for the build-up and maintenance of a complete catalog of space debris in the upper part of the low Earth orbits region (LEO). The purpose is to determine the achievable performances of a network of advanced optical sensors, through the use of the newest orbit determination algorithms developed by the Department of Mathematics of Pisa (DM). Such a network was designed and proposed to the European Space Agency (ESA) in the Space Situational Awareness (SSA) framework by Carlo Gavazzi Space SpA (CGS), Istituto Nazionale di Astrofisica (INAF), DM and Istituto di Scienza e Tecnologie dell'Informazione (ISTI-CNR). The latest developed orbit determination algorithms were used to process simulated observations from the proposed network. In particular two innovative methods for preliminary orbit determination based on the first integrals of the Kepler problem were compared, by using them to process the same data. In both cases, the results showed that it is possible to use a network of optical sensors to build up a catalog containing more than 98% of the objects with perigee height between 1100 and 2000 km, and diameter greater than 8 cm. Such a catalog is obtained in just two months of observations. However, such results depend upon specific assumptions on the sensor and on the software technologies
Symbolic dynamics for the -centre problem at negative energies
We consider the planar -centre problem, with homogeneous potentials of
degree -\a<0, \a \in [1,2). We prove the existence of infinitely many
collisions-free periodic solutions with negative and small energy, for any
distribution of the centres inside a compact set. The proof is based upon
topological, variational and geometric arguments. The existence result allows
to characterize the associated dynamical system with a symbolic dynamics, where
the symbols are the partitions of the centres in two non-empty sets
Orbit Determination with the two-body Integrals. II
The first integrals of the Kepler problem are used to compute preliminary
orbits starting from two short observed arcs of a celestial body, which may be
obtained either by optical or radar observations. We write polynomial equations
for this problem, that we can solve using the powerful tools of computational
Algebra. An algorithm to decide if the linkage of two short arcs is successful,
i.e. if they belong to the same observed body, is proposed and tested
numerically. In this paper we continue the research started in [Gronchi,
Dimare, Milani, 'Orbit determination with the two-body intergrals', CMDA (2010)
107/3, 299-318], where the angular momentum and the energy integrals were used.
A suitable component of the Laplace-Lenz vector in place of the energy turns
out to be convenient, in fact the degree of the resulting system is reduced to
less than half.Comment: 15 pages, 4 figure
Orbit determination with the two-body integrals
We investigate a method to compute a finite set of preliminary orbits
for solar system bodies using the first integrals of the Kepler problem. This method is thought for the applications to the modern
sets of astrometric observations, where often the information
contained in the observations allows only to compute, by interpolation,
two angular positions of the observed body and their time derivatives
at a given epoch; we call this set of data attributable.
Given two attributables of the same body at two different epochs we
can use the energy and angular momentum integrals of the two-body
problem to write a system of polynomial equations for the topocentric
distance and the radial velocity at the two epochs. We define two
different algorithms for the computation of the solutions, based on
different ways to perform elimination of variables and obtain a
univariate polynomial.
Moreover we use the redundancy of the data to test the hypothesis
that two attributables belong to the same body (linkage problem).
It is also possible to compute a covariance matrix, describing the
uncertainty of the preliminary orbits which results from the
observation error statistics.
The performance of this method has been investigated by using a large
set of simulated observations of the Pan-STARRS project.
We expect that this method can be used when the two epochs are well
separated, even if the time span is such that the algorithms based
upon propagation of a swarm of virtual objects become inadequate
Orbit determination for the radio science experiment of the NASA mission Juno
Juno is a NASA New Frontiers mission to the planet Jupiter, launched from Cape Canaveral on August 5,
2011. The spacecraft will arrive to Jupiter in 2016 and will be placed for one year in a polar high-eccentric
orbit to study the composition of the planet, the gravity and the magnetic field, and the magnetosphere. The
Italian Space Agency (ASI) contributed to the mission providing the radio science instrument KaT (Ka-Band
Translator, developed by the University of Rome “La Sapienza” and Thales Alenia Space) used for the gravity
experiment, which has the goal of studying the Jupiter’s deep structure by mapping the planet’s gravity. Such
instrument takes advantage of synergies with a similar tool in development for BepiColombo, the ESA cornerstone
mission to Mercury. The Celestial Mechanics Group of the University of Pisa and SpaceDyS s.r.l. are responsible,
under an ASI contract, for the development of an orbit determination and parameters estimation software for
processing the real data independently from NASA software ODP. We shall present the state of the art of such
software highlighting the theoretical models used, the problems addressed and first results about the scientific
goals obtained with simulated data